Ischemia promotes calpain-mediated degradation of p120-catenin in SH-SY5Y cells

The role of ubiquitination and deubiquitination in the regulation of cell junctions

Maintenance of cell junctions plays a crucial role in the regulation of cellular functions including cell proliferation, permeability, and cell death. Disruption of cell junctions is implicated in a variety of human disorders, such as inflammatory diseases and cancers. Understanding molecular regulation of cell junctions is important for development of therapeutic strategies for intervention of human diseases. Ubiquitination is an important type of post-translational modification that primarily regulates endogenous protein stability, receptor internalization, enzyme activity, and protein-protein interactions. Ubiquitination is tightly regulated by ubiquitin E3 ligases and can be reversed by deubiquitinating enzymes. Recent studies have been focusing on investigating the effect of protein stability in the regulation of cell-cell junctions. Ubiquitination and degradation of cadherins, claudins, and their interacting proteins are implicated in epithelial and endothelial barrier disruption. Recent studies have revealed that ubiquitination is involved in regulation of Rho GTPases’ biological activities. Taken together these studies, ubiquitination plays a critical role in modulating cell junctions and motility. In this review, we will discuss the effects of ubiquitination and deubiquitination on protein stability and expression of key proteins in the cell-cell junctions, including junction proteins, their interacting proteins, and small Rho GTPases. We provide an overview of protein stability in modulation of epithelial and endothelial barrier integrity and introduce potential future search directions to better understand the effects of ubiquitination on human disorders caused by dysfunction of cell junctions.

Effects of cerebrolysin on motor-neuron-like NSC-34 cells

Although the peripheral nervous system is capable of regeneration, this capability is limited. As a potential means of augmenting nerve regeneration, the effects of cerebrolysin (CL)--a proteolytic peptide fraction--were tested in vitro on the motor-neuron-like NSC-34 cell line and organotypic spinal cord cultures. Therefore, NSC-34 cells were subjected to mechanical stress by changing media and metabolic stress by oxygen glucose deprivation. Afterwards, cell survival/proliferation using MTT and BrdU-labeling (FACS) and neurite sprouting using ImageJ analysis were evaluated. Calpain-1, Src and α-spectrin protein expression were analyzed by Western blot. In organotypic cultures, the effect of CL on motor neuron survival and neurite sprouting was tested by immunohistochemistry. CL had a temporary anti-proliferative but initially neuroprotective effect on OGD-stressed NSC-34 cells. High-dosed or repeatedly applied CL was deleterious for cell survival. CL amplified neurite reconstruction to limited extent, affected calpain-1 protein expression and influenced calpain-mediated spectrin cleavage as a function of Src expression. In organotypic spinal cord slice cultures, CL was not able to support motor neuron survival/neurite sprouting. Moreover, it hampered astroglia and microglia activities. The data suggest that CL may have only isolated positive effects on injured spinal motor neurons. High-dosed or accumulated CL seemed to have adverse effects in treatment of spinal cord injury. Further experiments are required to optimize the conditions for a safe clinical administration of CL in spinal cord injuries.

p120catenin alteration in cancer and its role in tumour invasion

Since its discovery in 1989 as a substrate of the Src oncogene, p120catenin has been revealed as an important player in cancer initiation and tumour dissemination. p120catenin regulates a wide range of cellular processes such as cell-cell adhesion, cell polarity and cell proliferation and plays a pivotal role in morphogenesis, inflammation and innate immunity. The pleiotropic effects of p120catenin rely on its interactions with numerous partners such as classical cadherins at the plasma membrane, Rho-GTPases and microtubules in the cytosol and transcriptional modulators in the nucleus. Alterations of p120catenin in cancer not only concern its expression level but also its intracellular localization and can lead to both pro-invasive and anti-invasive effects. This review focuses on the p120catenin-mediated pathways involved in cell migration and invasion and discusses the potential consequences of major cancer-related p120catenin alterations with respect to tumour spread.

Calpain inhibitors exhibit matrix metalloproteinase-2 inhibitory activity

Matrix metalloproteinase (MMP)-2 is a zinc-dependent endopeptidase which, alongside its known extracellular actions, plays fundamental roles in oxidative stress-induced injury to the heart. Intracellular cleavage targets of MMP-2 selectively mediating this injury include the sarcomeric proteins troponin I, myosin light chain-1 and titin; some of these are also targeted by calpains. In myocardial ischemia and reperfusion injury, inhibitors of MMP-2 and some calpain inhibitors were shown to improve the recovery of contractile function. We hypothesized that the protective effects of calpain inhibitors may be due in part to their ability to inhibit MMP-2. Four calpain inhibitors (calpain inhibitor III, ALLM, ALLN, and PD-150606) were tested for their ability to inhibit MMP-2 in comparison to the selective MMP inhibitor ONO-4817. At 100 μM, all calpain inhibitors, except ALLM, showed significant inhibition of MMP-2 gelatinolytic activity. When assessed by the troponin I proteolysis assay, both ALLN and PD-150606, but neither ALLM nor calpain inhibitor III (at 20 μM), significantly inhibited MMP-2 activity. Using a fluorogenic MMP substrate peptide OmniMMP in a kinetic assay the rank order of IC(50) values against MMP-2 were: PD-150606<ALLN<calpain inhibitor III <<< ALLM. These experiments show that the calpain inhibitors PD-150606 and ALLN have significant additional pharmacological activity as MMP-2 inhibitors. This suggests that the protective effect of some calpain inhibitors is due in part to their ability to inhibit MMP activity.

Liver X receptor activation enhances blood-brain barrier integrity in the ischemic brain and increases the abundance of ATP-binding cassette transporters ABCB1 and ABCC1 on brain capillary cells

The blood-brain barrier (BBB) consists of dense contacts between endothelial cells, the tight junctions, which are complemented by membrane-bound transporters belonging to the ATP-binding cassette (ABC) transporter family. Liver X receptors (LXR) have previously been shown to stabilize the integrity of atherosclerotic noncerebral arteries. Their effects on ischemic cerebral vessels are still unknown. By delivering LXR agonists, T0901317 and GW3965, to mice submitted to 30 minutes intraluminal middle cerebral artery occlusion, we show that LXR activation reduces brain swelling and decreases BBB permeability by upregulating LXR's target calpastatin that deactivates calpain-1/2, stabilizing p120 catenin. p120 catenin specifically interacts with RhoA and Cdc42, inactivating the former and overactivating the latter, thus restoring the postischemic expression, phosphorylation and interaction of the tight junction proteins occludin and zona occludens-1. Moreover, LXR activation deactivates matrix metalloproteases-2/9 and inhibits microvascular apoptosis by deactivating JNK1/2 and caspase-3. In addition to the cholesterol transporters ABCA1 and ABCG1, which have previously been shown to be upregulated by LXR in noncerebral vessels, LXR activation increases the abundance of the drug transporters ABCB1 and ABCC1 on ischemic brain capillaries, as we further show. That LXR activation promotes endothelial integrity in different ways makes this receptor attractive as target for stroke therapies.

Cyclic stretch induces alveolar epithelial barrier dysfunction via calpain-mediated degradation of p120-catenin

Lung hyperinflation is known to be an important contributing factor in the pathogenesis of ventilator-induced lung injury. Mechanical stretch causes epithelial barrier dysfunction and an increase in alveolar permeability, although the precise mechanisms have not been completely elucidated. p120-catenin is an adherens junction-associated protein that regulates cell-cell adhesion. In this study, we determined the role of p120-catenin in cyclic stretch-induced alveolar epithelial barrier dysfunction. Cultured alveolar epithelial cells (MLE-12) were subjected to uniform cyclic (0.5 Hz) biaxial stretch from 0 to 8 or 20% change in surface area for 0, 1, 2, or 4 h. At the end of the experiments, cells were lysed to determine p120-catenin expression by Western blot analysis. Immunofluorescence staining of p120-catenin and F-actin was performed to assess the integrity of monolayers and interepithelial gap formation. Compared with unstretched control cells, 20% stretch caused a significant loss in p120-catenin expression, which was coupled to interepithelial gap formation. p120-Catenin knockdown with small interfering RNA (siRNA) dose dependently increased stretch-induced gap formation, whereas overexpression of p120-catenin abolished stretch-induced gap formation. Furthermore, pharmacological calpain inhibition or depletion of calpain-1 with a specific siRNA prevented p120-catenin loss and subsequent stretch-induced gap formation. Our findings demonstrate that p120-catenin plays a critical protective role in cyclic stretch-induced alveolar barrier dysfunction, and, thus, maintenance of p120-catenin expression may be a novel therapeutic strategy for the prevention and treatment of ventilator-induced lung injury.

Innate immune function of the adherens junction protein p120-catenin in endothelial response to endotoxin

Sepsis-induced acute lung injury is a common clinical disorder in critically ill patients that is associated with high mortality. In this study, we investigated the role of p120-catenin (p120), a constituent of endothelial adherens junctions, in regulating the innate immune function of lungs. In mice in which acute lung injury was induced by i.p. administration of LPS, we observed a rapid decrease in the expression of p120 in lungs. The p120 protein expression was correlated inversely with severity of inflammation. Suppression of p120 expression in lung endothelial cells in mice using small interfering RNA resulted in high sensitivity to endotoxin and greatly increased the mortality compared with controls. Knockdown of p120 also increased the expression of ICAM-1, neutrophil recruitment, production of cytokines TNF-α and IL-6, pulmonary transvascular protein permeability, and lung water content in response to LPS. We demonstrated that endothelial p120 modulates lung innate immune function by interfering with the association of TLR4 with its adaptor MyD88 to block TLR4 signaling and NF-κB activation in endothelial cells. In conclusion, these studies have uncovered a novel innate immune function of endothelial p120 in downregulating the lung inflammatory response to endotoxin through the suppression of TLR4 signaling.

Calpain activation contributes to endotoxin-induced diaphragmatic dysfunction

Calpain activation occurs in skeletal muscle in response to infection, but it is unknown if calpain inhibition improves muscle functional capacity. We hypothesized that infection induces diaphragm calpain activation, that calpain activation results in cleavage of important diaphragm cytoskeletal proteins, and that inhibition of calpain attenuates infection-induced diaphragm dysfunction. Mice (n = 4-6/group) were given: (1) saline (intraperitoneal); (2) endotoxin (12 mg/kg intraperitoneal); (3) calpain inhibitor peptide III (12 mg/kg intraperitoneal); and (4) endotoxin (12 mg/kg) plus calpain inhibitor peptide III (12 mg/kg). At 24 hours, diaphragms were removed and the following determined: (1) calpain activity by fluorogenic assay; (2) calpain I and II protein levels; (3) talin protein levels; and (4) the force-frequency relationship. Endotoxin significantly increased diaphragm calpain activity (P < 0.001), active calpain I protein (P < 0.001), active calpain II protein (P < 0.01), levels of a calpain-specific cleavage talin degradation product (P < 0.003), and reduced diaphragm force (P < 0.001). Calpain inhibitor III administration prevented endotoxin-induced increases in calpain activity, reduced talin degradation, and attenuated reductions in diaphragm force. Diaphragm-specific force at 150 Hz stimulation was significantly higher in control, endotoxin plus calpain inhibitor III, and calpain inhibitor III alone groups (23 +/- 1, 20 +/- 1 and 23 +/- 1 N/cm(2), respectively) than in the endotoxin alone group (15 +/- 1 N/cm(2)) (P < 0.01). This model of sepsis results in significant diaphragm calpain activation and calpain-dependent diaphragm cytoskeletal protein cleavage. Moreover, calpain inhibition attenuates endotoxin-induced diaphragm weakness, suggesting that such inhibitors may be a potential treatment to improve respiratory muscle function in infected patients.

Calpain-mediated signaling mechanisms in neuronal injury and neurodegeneration

Calpain is a ubiquitous calcium-sensitive protease that is essential for normal physiologic neuronal function. However, alterations in calcium homeostasis lead to persistent, pathologic activation of calpain in a number of neurodegenerative diseases. Pathologic activation of calpain results in the cleavage of a number of neuronal substrates that negatively affect neuronal structure and function, leading to inhibition of essential neuronal survival mechanisms. In this review, we examine the mechanistic underpinnings of calcium dysregulation resulting in calpain activation in the acute neurodegenerative diseases such as cerebral ischemia and in the chronic neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis, prion-related encephalopathy, and amylotrophic lateral sclerosis. The premise of this paper is that analysis of the signaling and transcriptional consequences of calpain-mediated cleavage of its various substrates for any neurodegenerative disease can be extrapolated to all of the neurodegenerative diseases vulnerable to calcium dysregulation.